In the mobile communication system, a radio communication mobile station apparatus (hereinafter “mobile station”) performs a cell search upon power activation or upon handover. This cell search is performed using an SCH (synchronization channel). The SCH is a shared channel in the downlink direction and is comprised of a P-SCH (primary synchronization channel) and an S-SCH (secondary synchronization channel). P-SCH data contains a sequence which is common in all cells and which is used for the timing synchronization upon the cell search. Further, S-SCH data contains cell-specific transmission parameters such as scrambling code information. In a cell search upon power activation or upon handover, each mobile station finds the timing synchronization by receiving P-SCH data and acquires transmission parameters that differ between cells by receiving S-SCH data. By this means, each mobile station can start communicating with radio communication base station apparatuses (hereinafter “base stations”). Therefore, each mobile station needs to detect SCH data upon power activation or upon handover.
Further, according to the FFD scheme standard proposed by 3GPP, frequencies for setting carriers are arranged at 200 kHz intervals in a 60 MHz frequency bandwidth (see Patent Document 1). Therefore, according to this standard, the frequency interval the mobile station performs a cell search is 200 kHz. That is, the mobile station performs a cell search every 200 kHz.
Further, to simplify the design of the communication system, the SCH is generally set in the center frequency of the frequency bandwidth in which a mobile station can perform communication.
By the way, in recent years, in mobile communication, various kinds of information such as images and data as well as speech are subjected to transmission. With this trend, it is expected that demands further increase for high reliability and high speed transmission. However, when high speed transmission is performed in mobile communication, the influence of delayed waves by multipath is not negligible, and transmission performance degrades due to frequency selective fading.
Multicarrier communication such as OFDM (Orthogonal Frequency Division Multiplexing) has attracted attention as one of counter techniques for frequency selective fading. Multicarrier communication refers to a technique of performing high speed transmission by transmitting data using a plurality of subcarriers of transmission rates suppressed to such an extent that frequency selective fading does not occur. Particularly, with the OFDM scheme, frequencies of a plurality of subcarriers where data is arranged are orthogonal to each other, thereby enabling the maximum frequency efficiency in multicarrier communication and implementation with relatively simple hardware configuration. By this means, the OFDM scheme has attracted attention as a communication method applied to cellular scheme mobile communication and is variously studied. In the communication system employing the OFDM scheme, the interval between adjacent subcarriers (subcarrier intervals) in a plurality of subcarriers, is set according to the coherence bandwidth (the frequency bandwidth in which channel fluctuation is the same) of this communication system.
Further, at present, according to the LTE standardization of 3GPP, in the mobile communication system with the OFDM scheme, allowing a plurality of mobile stations communicating in respective bandwidths, to perform communication in the system, is studied. This mobile communication system can be referred to as a “scalable bandwidth communication system.”
For example, assuming the scalable bandwidth communication system having a 20 MHz operating frequency bandwidth, if the 20 MHz operating frequency bandwidth is equally divided per 5 MHz frequency bandwidth into four frequency bands FB1 FB2, FB3 and FB4, it is possible to use mobile stations having 5 MHz, 10 MHz or 20 MHz communication capacities at the same time. In the following explanation, out of a plurality of mobile stations that are available, the mobile station having the minimum communication capacity is referred to as the “minimum capacity mobile station,” and the mobile station having the maximum communication capacity is referred to as the “maximum capacity mobile station.” Therefore, in this case, the mobile station having the 5 MHz communication capacity is the minimum capacity mobile station and the mobile station having the 20 MHz communication capacity is the maximum capacity mobile station.
Further, for example, assuming the scalable bandwidth communication system with a 4.2 MHz operating frequency bandwidth, if the 4.2 MHz operating bandwidth is divided per 2.1 MHz frequency bandwidth into two bandwidths FB1 and FB2, it is possible to use a mobile station having a 2.1 MHz communication capacity and a mobile station having a 4.2 MHz communication capacity at the same time. Therefore, in the above, the mobile station having a 2.1 MHz communication capacity is the minimum capacity mobile station and the mobile station having a 4.2 MHz communication capacity is the maximum capacity mobile station. A mobile station having a 2.1 MHz communication capacity is referred to as a “2.1 MHz mobile station,” and a mobile station having a 4.2 MHz communication capacity is referred to as a “4.2 MHz mobile station.” In this scalable bandwidth communication system, the 2.1 MHz mobile station is assigned a 2.1 MHz frequency bandwidth out of the 4.2 MHz frequency bandwidth and performs communication. That is, the 2.1 MHz mobile station is assigned one of FB1 and FB2 and performs communication. Further, the 4.2 MHz mobile station can perform high speed communication using the entire 4.2 MHz operating frequency bandwidth. Here, as described above, the frequency bandwidth, in which the maximum capacity mobile station can perform communication, generally matches the frequency bandwidth where a scalable bandwidth communication system is operated (in this case, 4.2 MHz).    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-60551